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Full text of "Handbook Of Chemical Engineering - I"

152
CHEMICAL ENGINEERING
given weight (col. 2) and on the weight of a given volume (col. 3) of air; on the pressures (cols. 2 and 3) corresponding to constant weight and constant volume, respectively, of air handled by a fan; on the speeds (cols. 2 and 4) corresponding to constant weight and constant pressure, respectively, of air handled by a fan; on the power (cols. 3 and 5) corresponding to constant volume and constant weight, respectively, of air handled by a fan; and the power (col. 2) necessary to handle a given weight at a given pressure with a fan proportioned to operate at a given efficiency. All these factors are to be applied to the quantities corresponding to the standard air temperature of 65°F
TABLE 11.__FACTORS FOR DETERMINING THE PERFORMANCE OF FANS AT  VARIOUS
AIR TEMPERATURES (SEE TEXT)
Temperature, degrees Fahrenheit	2	3	4	5	Temperature, degrees Fahrenheit	2	3	4	5
30	0.94	1.07	0.97	0.87	325	1.50	0.67	1.22	2.24
40	0.96	1.05	0.98	0.91	350	1.55	0.65	1.24	2.38
50	0.97	1.03	0.99	0.95	375	1.59	0.63	1.26	2.54
60	0.99	1.01	0.99	0.98	400	1.63	0.61	1.28	2.69
65	1.00	1.00	1.00	1.00	425	1.68	0.60	1.30	2.85
70	1.01	0.99	1.01	1.02	450	1.73	0.58	1.32	3.02
80	1.03	0.97	1.02	1.06	475	1.78	0.57	1.33	3.18
90	1.05	0.95	1.03	1.11	500	1.83	0.54	1.35	3.38
100	1.07	0.93	1.04	1.15	525	1.88	0.53	1.37	3.52
125	1.12	0.89	1.06	1.25	550	1.93	0.52	1.39	3.72
150	1.17	0.86	1.08	1.36	575	1.98	0.50	1.41	3.90
175	1.21	0.83	1.10	1.47	600	2.02	0.49	1.42	4.10
200	1.26	0.80	1.12	1.58	650	2.12	0.47	1.46	4.50
225	1.30	0.77	1.14	1.71	700	2.21	0.45	1.49	4.90
250	1.35	0.74	1.16	1.83	750	2.31	0.43	1*52	5.32
275	1.40	0.71	1.18	1.96	800	2.410.41		1.55	5.78
300	1.45	0.69	1.20	2.10				i i	
For-the weight of 1 cu. ft. of air at any temperature, pressure and humidity within the usual range, see page 143.
Fan Characteristics.—The characteristics of any fan can best be shown graphically. The characteristic curves from any size of a series of similar fans suffice for the entire group. This follows from the fact that the area of the frictional surfaces varies directly with the area of the various passages through which air flows when passing through the fan. The different bases upon which these characteristic curves can be plotted are as stated in the following paragraphs.
Static No Delivery (S.N.D.).—This gives a useful basis for calculating the performance of various fans. Figure 3 is the chart of a fan known as the "steelplate" or "paddle-wheel" type. Data for these curves are obtained by running the fan at some convenient constant speed and taking a set of readings at each of six to eight air deliveries produced by as many different restrictions placed on the discharge and varying from a condition of closed outlet to wide open or free discharge. All data are taken at the fan outlet. The abscissas are the static pressures or maintained resis-